Characterising the scale and significance of persistent organic pollutants in South African sediments

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Abstract

Water resources in South Africa are scarce, and should therefore be protected against pollutants,
also from persistent organic pollutants (POPs). POPs are a global concern due to their ubiquitous
presence, persistence and toxicity. This is emphasised by the Stockholm Convention on POPs,
which aims at reducing and ultimately eliminating them. South Africa signed and ratified the
treaty, and it became international law on 17 May 2004, but there is still a lack of information
regarding POPs in South Africa.
This study focussed on establishing the levels of POPs and other organic pollutants, which
included various organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs),
dioxin-like compounds (DLCs), non-dioxin-like polychlorinated biphenyls (PCBs) and
polybrominated diphenyl ether (PBDE). Sampling regions included the industrial cities – Cape
Town, Richards Bay, Durban and Bloemfontein, and low-income, high density residential areas
surrounding a wetland in Soweto/Lenasia and Botshabelo. Additionally, rivers flowing into
neighbouring countries, rivers in the vicinity of paper and pulp producers and high altitude rivers
were included. Sediment samples were firstly screened for the presence of DLCs by the H4IIE-luc
bio-assay, whereafter sites eliciting quantifiable responses were selected for further chemical
analysis by high resolution gas chromatography-high resolution mass spectrometry
(HRGC/HRMS).
Of the 96 sites, only 23 had quantifiable levels of DLCs. These sites were mainly of industrial,
semi-industrial or low-income residential nature. PAHs were the predominant class of compounds
at most of the sites, while OCPs and PCBs were present in moderate concentrations and PBDEs in
minor concentrations. The concentration of pollutants measured in South African soils and
sediments were intermediate when compared to the levels measured in some European, Asian and
Scandinavian countries, with the exception of a few sites where exceptionally high levels of
compounds were measured. The carbon content normalized concentrations of certain compounds
at some of the sites exceeded the Canadian sediment quality guidelines. The estimated cancer risk
associated with dermal absorption of OCPs measured in this study was negligible when compared
to the background cancer risk expected for South Africans due to life style factors. However, it
was estimated that dermal exposure to PCBs, DLCs and PAHs may lead to severe increases in
cancer cases, and may seriously impact on human health.